1. Field of the Invention
The present invention pertains to fire prevention systems for fuel tanks. In particular the present invention pertains to fire prevention systems for aircraft fuel tanks which are subject to penetration by high explosive incendiary projectiles or high velocity fragments.
2. Description of the Prior Art
Numerous military vehicles have a high vulnerability to penetration of their fuel tanks. The equipment bays or void spaces around and under fuel tanks, such as on aircraft, are vulnerable to fires if hit by high explosive incendiary projectiles, HEI. Such projectiles, penetrate the outer skin of the aircraft. This penetration triggers a fuse which detonates the projectiles explosive charge a short time later, usually a few microseconds. The projectile fragments into smaller pieces which are expelled at high velocities followed by the development of an incendiary fireball.
The fragments penetrate the fuel tank and fuel is expelled into the area where the incendiary fire is developing and is ignited. In order to prevent a fuel fire, all that is required is that no fuel be expelled for approximately ten milliseconds, which is the average duration of the incendiary fire.
Due to weight constraints on combat aircraft, any system for vulnerability reduction must be very lightweight and require little if any maintenance. Systems presently in use on aircraft are either complex fire sensing and extinguishing systems which are heavy and expensive or are systems which employ a foam buffer which has not been proven to have high reliability. Numerous examples of buffer systems around fuel tanks can be found in U.S. Pat. Nos. 3,698,597 to Burke, 3,924,773 to Wilkinson, 4,121,666 to Rozniecki, and 4,141,460 to Stanistreet et al. All of these patents can be considered considerable state-of-the-art advances over U.S. Pat. No. 2,404,418 to Walker. The Walker patent uses a rubber liner to protect fuel tanks punctured by bullets. The Walker patent uses pressurized containers within rubber liners to slow the fuel retardant forces. Collapse causes nonalignment of the punctures in the rubber liner and the fuel tank wall itself. However, as stated in the Walker patent, bullets are assumed to make sharp clean holes through the metal walls. Modern high explosive incendiaries produce jagged fragments which do not produce the same type of clean holes described in Walker. Such fragments literally shread a rubber liner. The Walker device is not suitable for aircraft because it takes up too much space needed for fuel and adds excessive weight.